Alex Spillius is The Daily Telegraph's Washington Correspondent.

Sarah Palin: John McCain's August surprise

Full coverage of the US Election 2008More on Sarah Palin. The merits and demerits of McCain's selection will become evident over the next few weeks, but credit is due to the campaign for pulling off a complete surprise without even the drop of a leak.

Mr McCain's choice of Ms Palin for running mate surprised everyone

Keeping her appointment quiet was of course easier because she was such a dark horse in a faraway place, but in the acres of speculation and card-marking over the past few weeks her name has only been mentioned occasionally. It was a major victory over the punditocracy.

Palin is an unknown quantity. On the morning flight back to Washington carrying delegates, congressional staffers and think tank types from Denver yesterday announced the decision in mid-air. Matt Bennett, a former staffer for Clinton and Gore, now with the Third Way, was on board. â€˜People were saying who? There was tremendous confusion.'

Bennett disagrees with the idea Joe Biden will have to hold fire on Palin in the vice-presidential debate, as many have been saying today.

He told me: â€˜Biden is likely to make her look like an amateur. The notion that he has to go easy on her is preposterous. After Hillary Clinton's campaign, voters are now acclimated to tough debate exchanges between men and women. That's one of the glass ceilings Clinton did shatter, they play on the same field with the boys and can take the same hits.'

We will see. I still think the preparation for Biden will be even more rigorous than usual: during 90 minutes uncut there is too much chance that he will drop a clanger – calling her â€˜sweetie' or a â€˜honey' or making some comment on her picturesque looks.